Description
The TinySwitch™ family uses a breakthrough design to provide
the lowest cost, high efficiency, off-line switcher solution in
the 0 to 10 W range. These devices integrate a 700 V power
MOSFET, oscillator, high-voltage switched current source,
current limit and thermal shutdown circuitry. They start-up
and run on power derived from the DRAIN voltage, eliminating
the need for a transformer bias winding and the associated
circuitry. And yet, they consume only about 80 mW at no load,
from 265 VAC input. A simple ON/OFF control scheme also
eliminates the need for loop compensation.
The TNY253 and TNY254 switch at 44 kHz to minimize EMI
and to allow a simple snubber clamp to limit DRAIN spike
voltage. At the same time, they allow use of low cost EE16 core
transformers to deliver up to 5 W. The TNY253 is identical to
TNY254 except for its lower current limit, which reduces output
short-circuit current for applications under 2.5 W. TNY255
uses higher switching rate of 130 kHz to deliver up to 10 W
from the same low cost EE16 core for applications such as PC
standby supply. An EE13 or EF13 core with safety spaced
bobbin can be used for applications under 2.5 W. Absence of
a bias winding eliminates the need for taping/margins in most
applications, when triple insulated wire is used for the secondary.
This simplifies the transformer construction and reduces cost.